String Operators

There are two string operators. The first is the
concatenation operator ('.'), which returns the concatenation of its
right and left arguments. The second is the concatenating assignment
operator ('.='), which appends the argument on the right side to
the argument on the left side. Please read Assignment
Operators for more information.

As for me, curly braces serve good substitution for concatenation, and they are quicker to type and code looks cleaner. Remember to use double quotes (" ") as their content is parced by php, because in single quotes (' ') you'll get litaral name of variable provided: